1. Field of the Invention
The present invention relates to an apparatus for feeding secondary air to exhaust gas in an engine, in which an exhaust port for discharging exhaust gas from a combustion chamber and a secondary air feed passage for feeding secondary air to exhaust gas flowing through the exhaust port are provided in a cylinder head of the engine.
2. Description of Related Art
An apparatus of this type has been known, for example, from Japanese Utility Model No. Sho 61-4009. The apparatus disclosed in the above document, however, is problematic. In this apparatus, a secondary air feed passage is provided in a cylinder head in such a manner as to extend substantially in parallel to the axial line of a cylinder bore and a reed valve is mounted in a head cover for covering the cylinder head. To be more specific, the secondary air feed passage is opened to an exhaust port in such a manner as to face toward exhaust gas flowing through the exhaust port, so that exhaust gas is liable to permeate into the secondary air feed passage. This results in the flow resistance in the secondary air feed passage possibly increasing by adhesion of carbon or the like on the inner surface of the secondary air feed passage. Furthermore, since the reed valve is prevented from being eroded by permeation of exhaust gas into the secondary air feed passage, the apparatus disclosed in the above document is configured such that the secondary air feed passage extending in a straight line is made relatively long and correspondingly the reed valve is disposed at a position relatively far from the cylinder head. This results in enlargement of the entire engine.